Edith Windsor, center, is interviewed at the offices of the New York Civil Liberties Union, in New York, Thursday, Oct. 18, 2012. A federal appeals court in Manhattan has become the second in the nation to strike down the Defense of Marriage Act as unconstitutional. The ruling came in a case brought by Windsor. She sued the government in November 2010 because she was told to pay $363,053 in federal estate tax after her partner of 44 years died in 2009. Her attorney Roberta Kaplan is at right. (AP Photo/Richard Drew)

Photo: Richard Drew, Associated Press

Edith Windsor, center, is interviewed at the offices of the New...

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The U.S. Supreme Court took up the issue of same-sex marriage Friday, agreeing to decide whether gays and lesbians can wed in California and whether the federal government can deny benefits to married same-sex couples.

Photo: J. Scott Applewhite, File Photos

The U.S. Supreme Court took up the issue of same-sex marriage...

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FILE - This Dec. 17, 2010 file photo shows Karen Golinski, right, hugging her wife Amy Cunninghis as they pose for a photograph outside of a federal court building in San Francisco. The fight over gay marriage is shifting from the ballot box to the Supreme Court.

The U.S. Supreme Court: Seated, from left: Clarence Thomas; Antonin...

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A ruling by the Supreme Court on DOMA could have implications across the nation, including Washington state, which just began process same-sex marriage applications. Photo by Meryl Schenker, used with permission.

Photo: Meryl Schenker

A ruling by the Supreme Court on DOMA could have implications...

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John Lewis (center) and Stuart Gaffney listen to San Francisco City Attorney Dennis Herrera discuss the court's moves.

Photo: Michael Macor, The Chronicle

John Lewis (center) and Stuart Gaffney listen to San Francisco City...

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State Attorney General Kamala Harris talks about the case. The state is not defending Prop. 8.

Photo: Michael Macor, The Chronicle

State Attorney General Kamala Harris talks about the case. The...

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San Francisco City Attorney Dennis Herrera talks about the Supreme Court decision to consider the constitutionality of California's Proposition 8. The city has joined the lawsuit against the law, which bans same-sex marriage in the state.

Photo: Michael Macor, The Chronicle

San Francisco City Attorney Dennis Herrera talks about the Supreme...

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Leaders in the freedom to marry movement, partners, John Lewis, (center) and Stuart Gaffney listen to comments from City Attorney Dennis Herrera during a press conference at City Hall in San Francisco, Calif. on Friday Dec. 7, 2012. The Supreme Court has decided to hear the case of Proposition 8 which was overturned by the California Supreme Court.

More than eight years after San Francisco's mayor told city clerks to ignore state law and issue marriage licenses to same-sex couples, and four years after gays and lesbians first won and then lost the right to wed in California, the burning question of who can marry in the state - and perhaps the nation - has reached the U.S. Supreme Court.

After weeks of indecision, the justices granted hearings Friday to supporters of California's Proposition 8, which defined marriage as the union of a man and a woman, and the 1996 federal law known as the Defense of Marriage Act. That law withholds federal recognition and spousal benefits, including joint tax filing, Social Security survivor payments and immigration sponsorship, from married same-sex couples. According to researchers, there may be 100,000 or more such couples in the nine states where same-sex marriage is legal, and in California, where 18,000 couples wed during a brief period of legality in 2008.

The cases will be heard in March or April, with rulings due by the end of June.

They will be argued before a court widely regarded as the most conservative in many decades - but one that includes justices who have ruled twice in favor of gay rights.

A 1996 ruling struck down Colorado's prohibition of local gay-rights ordinances, finding that the ban was unconstitutionally based on antagonism toward gays and lesbians. In 2003, the court overturned state laws against gay sexual activity as a violation of privacy and personal autonomy. Both rulings were written by Justice Anthony Kennedy, who may hold the deciding vote in the marriage cases.

Neither of the earlier cases set standards for reviewing other antigay laws or mentioned same-sex marriage, which was not yet legal in any state.

Times have changed

But times, and public opinion, have changed - most visibly in Maine, Maryland and Washington, whose voters on Nov. 6 became the first in the nation to legalize same-sex marriage in statewide referendums.

One constitutional law professor, David S. Cohen of Drexel University in Pennsylvania, said Friday that the court "has to be aware of the trend, and will not rule against equality, knowing what the future holds."

But the growing acceptance of same-sex marriage rights could also lead the justices to conclude that gays and lesbians are gaining enough support in the political system that they need no special judicial protection.

While the Supreme Court has agreed to decide the constitutionality of both Prop. 8 and the federal DOMA, it's not clear that either ruling will resolve the broader issue of whether the Constitution's guarantee of equal protection of the laws gives gays and lesbians equal marriage rights in all states.

The court could reach that issue, particularly if it upholds one or both laws and decides that states and the federal government can refuse to recognize same-sex unions. The justices could also take the narrower approach of the federal appeals courts that struck down both Prop. 8 and DOMA without deciding whether same-sex couples have a constitutional right to marry.

Prop. 8, approved by 52 percent of the voters in November 2008, amended the California Constitution to overturn a May 2008 ruling by the state Supreme Court that legalized same-sex marriage.

In February, the Ninth U.S. Circuit Court of Appeals ruled that Prop. 8 had withdrawn rights from a historically protected minority for no apparent reason other than moral disapproval of homosexuality - an unconstitutional act, the court said, under the Supreme Court's precedent in the 1996 Colorado case.

On Friday, Andy Pugno, chief counsel for the conservative religious coalition called Protect Marriage that sponsored Prop. 8, said the Supreme Court will now be able to "uphold the will of more than 7 million Californians who voted to preserve the unique definition of marriage as only between one man and one woman."

Theodore Olson, lawyer for the American Foundation for Equal Rights and two same-sex couples who challenged Prop. 8, countered that the court's review "brings us closer to the day when every American will be able to equally enjoy the fundamental freedom to marry."

Setting things in motion

The court's order also resonated in San Francisco, where then-Mayor Gavin Newsom defied the state's ban on same-sex marriage in 2004 - authorizing nearly 4,000 weddings that were soon nullified by the state Supreme Court, but setting in motion the legal case now before the nation's highest court.

"I have every confidence that come summertime, we will once again be on the right side of history," said City Attorney Dennis Herrera, who has joined the suit against Prop. 8.

The ban on same-sex marriage remains in effect while the case is on appeal.

Also still in effect is the Defense of Marriage Act, despite rulings by a half-dozen federal courts, including two Bay Area judges, holding it unconstitutional.

Those courts have concluded that the federal government, which has historically respected states' definitions of marriage, discriminated against gays and lesbians by denying them benefits from state-recognized marriages.

The Supreme Court granted review in the case of Edith Windsor, an 83-year-old New York woman who was ordered to pay more than $363,000 in estate taxes after the death of her wife, Thea Spyer. Windsor would have been exempt from the tax if the federal government had recognized their marriage.

The court also left open the possibility of avoiding a decision in either case by asking for arguments on whether backers of the two laws - Protect Marriage for Prop. 8, and a House Republican-led group for DOMA - have standing, or the legal authority to defend the measures in court.

Protect Marriage stepped in after California's top officials, including then-Attorney General and now-Gov. Jerry Brown, declined to defend Prop. 8. House Republicans intervened after President Obama withdrew support from DOMA and sided with the law's opponents.

Lower courts have ruled that both groups have standing to defend the laws. If the Supreme Court disagrees, it could dismiss the cases without ruling on the merits - an action that, in the Prop. 8 case, would clear the way for same-sex marriages in California.

The cases are Hollingsworth vs. Perry, 12-144, and U.S. vs. Windsor, 12-307.

What's next

Hearings: In March or April, the Supreme Court will hear arguments on the constitutionality of California's Proposition 8, which banned same-sex marriage in the state, and the federal Defense of Marriage Act, which denied federal benefits to legally married same-sex couples.

Ruling: Rulings are due by late June, the end of the court's 2012-13 term. If Prop. 8 is overturned, gays and lesbians will be allowed to marry in California. If DOMA is struck down, as many as 100,000 couples will be entitled to federal benefits.

In the meantime: Prop. 8 remains in effect, barring same-sex marriages in California and denying state recognition to such marriages performed in other states or countries after the measure passed in November 2008. DOMA also remains in effect.